1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and its driving method.
2. Description of Related Art
PDPs are display panels in which a pair of substrates formed with discharge electrodes thereon is disposed in an opposed relation and is sealed at the periphery to form a discharge space inside. The PDPs need a relatively high drive voltage for generating discharge. For this reason, they require a drive circuit (driver) with a high voltage resistance and a high capacity, and consequently, its production costs are high. Also, power consumption is large.
To cope with such problems, various countermeasures have been proposed. However, in the PDPs, the drive voltage cannot be decreased greatly because it is determined by discharge which is a physical phenomenon.
In the PDPs, the power consumption is the sum of power consumption required for charging inter-electrode capacity, power consumption required for discharge, and power consumption required by the drive circuit.
Among them, the power consumption required for charging the inter-electrode capacity is referred to as reactive power. A power collecting technique allows this power to be re-used to some extent for the purpose of reducing the power consumption. The power consumption required by the drive circuit is determined by the drive voltage. The power consumption required for discharge is represented by the drive voltage multiplied by electric current flowing into the discharge space by discharge. This is explained by taking an AC-driven PDP for example. First, a panel structure of the AC-driven PDP is described.
FIG. 44 is a perspective view partially illustrating the structure of a typical AC-driven three-electrode surface-discharge PDP. As shown in this figure, a PDP 10 is composed of a front panel assembly including a front substrate 11 and a rear panel assembly including a rear substrate 21. The front substrate 11 and the rear substrate 21 are formed of glass.
Electrodes X and Y formed on an inside surface of the front substrate 11 are for generating a surface discharge for display between a pair of electrodes X and Y. The electrodes X and Y are each formed of a wide transparent electrode 12 of ITO, SnO2 or the like and a narrow bus electrode 13 for reducing the resistance of the electrode. The bus electrode 13 is formed of a metal such as Ag, Au, Al, Cu, Cr, their laminate (e.g. a laminate of Cr/Cu/Cr) or the like. The electrodes X and Y are formed in a desired number to a desired thickness and width at desired intervals by utilizing a printing method for Ag and Au and by combining a film forming method such as vapor deposition, sputtering or the like with an etching method for other materials. Either the electrodes X or Y are used as scan electrodes.
A dielectric layer 17 is formed by applying a glass paste containing a low-melting glass frit, a binder and a solvent onto the front substrate 11 by a screen printing method, followed by burning.
On the dielectric layer 17, a protective film 18 is mounted for protecting the dielectric layer 17 from damage owing to impact of ions generated by discharge at display operation. The protective film 18 is formed of MgO, CaO, SrO, BaO or the like, for example.
Address electrodes A are formed on an inside surface of the rear substrate 21 so as to cross the electrodes X and Y. The address electrodes A are for generating an address discharge where the address electrodes cross the scanning electrodes X or Y. The address electrodes A are formed of Ag, Au, Al, Cu, Cr, their laminate (e.g. a laminate of Cr/Cu/Cr) or the like, for example. The address electrodes A, like the electrodes X and Y, are formed in a desired number to a desired thickness and width at desired intervals by utilizing the printing method for Ag and Au and by combining a film forming method such as vapor deposition, sputtering or the like with the etching method for other materials.
A dielectric layer 24 is formed of the same material by the same method as the dielectric layer 17.
Barrier ribs 29 can be formed on the dielectric layer 24 between the address electrodes by a sandblasting method, a printing method, a photo-etching method or the like. For example, they may be formed by applying a glass paste containing a low-melting glass frit, a binder, a solvent and the like onto the dielectric layer 24, drying it, cutting it by the sandblasting method and burning. Alternatively, the barrier ribs 29 can be formed with use of a photo-conductive resin as the binder, which is exposed using a mask and developed, followed by burning.
Fluorescent layers 28R, 28G and 28B can be formed by applying a phosphor paste containing a phosphor powder and a binder into grooves between the barrier ribs 29 by use of a screen printing method or a dispenser repeatedly for every color, followed by burning. Also, these fluorescent layers 28R, 28G and 28B can be formed with use of sheet-form materials (so-called green sheets) for the fluorescent layers containing phosphor powders and a binder by a photolithographic method. In this case, a sheet of a desired color is attached over a display area on the substrate, exposed and developed. This process is repeated for every color, thereby forming the fluorescent layers of the respective colors in corresponding grooves between the barrier ribs.
The PDP 10 is produced by placing the above-described front and rear panel assemblies in the opposed relation so that the electrodes X and Y are orthogonal to the address electrodes, sealing the periphery and feeding a discharge gas of neon, xenon and the like into spaces surrounded by the barrier ribs 29. In this PDP 10, a discharge space at the crossing of one pair of electrodes X and Y and one address electrode is one cell region (unit light-emitting region) which is the minimum unit of display.
In this AC-driven PDP 10, a discharge phenomenon across electrodes terminates spontaneously as a cell voltage (voltage applied to the discharge space) declines by the formation of a wall charge (an electric charge formed on a surface of the dielectric layer facing the discharge space). The amount of the wall charge formed at this time is an amount such that the cell voltage becomes a xe2x80x9c0.xe2x80x9d That is, with regard to the discharge across the electrodes X and Y, if +E (V) and 0 (V) are applied to the electrodes X and Y, respectively, the wall charge is so formed to have a potential of +E/2 (V) on the surface of the dielectric layer on the electrode.
If a capacity of C (F) is formed between the electrode and the surface of the dielectric layer on the electrode, a charge Qx=CE/2 (C) is formed on the surface of the dielectric layer above the electrode X and a charge Qy=xe2x88x92CE/2 (C) is formed on the surface of the dielectric layer above the electrode Y. Accordingly, if a drive frequency is f, a discharge current I can be represented by I=CE2f because the period of discharge is 2f. A power consumption P is P=CE2f because P=voltagexc3x97current. As understood from the above, a reduction in the voltage E and a reduction in the capacity C are necessary for reducing the power consumption at the discharge.
As measures to reduce the capacity C, the area of electrodes can be decreased, the thickness of the dielectric layer can be increased, the dielectric constant of the dielectric layer can be decreased and the like. However, a decrease in the area of electrodes and an increase in the thickness of the dielectric layer result in a rise in the drive voltage. As regards a decrease in the dielectric constant of the dielectric layer, it is necessary to develop a new dielectric having a low dielectric constant. Therefore, in order to reduce the power consumption at the discharge, the drive voltage needs to be decreased without a decrease in an electrode voltage.
The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a plasma display panel and its driving method by inserting a capacity element for raising voltage between electrodes and a drive circuit, and utilizing a charge stored in the capacity element for obtaining a high electrode voltage with a low drive voltage, thereby reducing the power consumption.
The present invention provides a plasma display panel comprising at least one pair of discharge electrodes disposed on a substrate; a drive circuit for applying a discharge voltage for generating discharge to the discharge electrodes; capacity elements for raising voltage connected in series between the discharge electrodes and the drive circuit; and a control circuit for generating the discharge across the discharge electrodes, the control circuit applying a charging voltage to the capacity elements for raising voltage and thereafter applying the discharge voltage from the drive circuit to the discharge electrodes via the capacity elements or raising voltage.
According to the present invention, when the discharge is generated across the discharge electrodes, voltage by the charge stored in the capacity element for raising voltage is added to the discharge voltage applied from the drive circuit. This voltage in total is applied to the discharge electrodes. Thus, the discharge can be produced by lower drive voltage than in a PDP without the capacity elements for raising voltage. Thereby, a load on the drive circuit, the power consumption and costs of the drive circuit can be reduced.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.